The present invention relates to a concentrator system for connecting geographically scattered subscriber terminals to the public switched telecommunication network through limited channel resources. More specifically, the invention relates to such a concentrator system in which emergency calls to police departments or fire stations are completed through a specially reserved channel.
Radio concentrator systems have been developed as an economic means for connecting remotely located subscriber terminals, such as telephones and data terminals, to an access point of the public switched telephone network through demand-assigned time division access channels. The system comprises a central station located relatively close to the access point of the network and a plurality of remote stations to which the subscriber terminals are connected by groups. Because of the limited number of demand-assigned channels, congestion tends to occur at peak traffic loads. With prior art radio concentrator systems, an emergency call from ordinary subscribers is treated as an ordinary call and routed through one of the demand-assigned channels if it is available. The prior art system is provided with one or more channels which are specially preassigned to special subscribers to allow them to complete an emergency call under congested traffic. However, an emergency call from ordinary subscribers must be abandoned when it encounters a condition indicating that all channels are busy.